Both the ability of atmospheric aerosols (haze, smoke, dust) to serve as seeds for cloud droplets and to scatter sunlight are largely influenced by particle size and type, which vary on regional scales. Hygroscopic particles grow with increasing relative humidity and liquid water can comprise over half of the particle volume under humid conditions typical of summer Southeastern U.S. Field campaigns in the SE U.S. also highlighted the importance of aqueous phase secondary organic aerosol production. While several long-term datasets of aerosol hygroscopic growth and CCN concentrations exist in Europe, the paucity of such measurements in the U.S and Asia necessitates estimates inferred from more commonly measured aerosol optical properties (AOPs) to achieve the necessary spatiotemporal coverage to improve climate models and evaluate satellite-based retrievals. This presentation will highlight results from the first long-term simultaneous measurements of aerosol hygroscopicity and cloud condensation nuclei in the southeastern U.S.